Gasket and method for high-temperature and high pressure application

ABSTRACT

A gasket including a sheet having a composition of 40 to 80% by weight of thin flakes of expanded vermiculite, 1 to 30% by weight of fibers, 5 to 40% by weight of fine filling grains, and appropriate amounts of a binding agent and a vulcanizing agent. The sheet also has a metal plate laminated thereto. A vortex gasket may be formed by spirally winding a metal hoop together with a filling material, which is composed primarily of expanded vermiculite.

The present invention relates generally to a gasket, and moreparticularly to a gasket such as that used in a high-temperature andpressure atmosphere, or to a vortex gasket, which is a modified versionthereof. The invention is also concerned with a method for thepreparation of said gaskets.

Gaskets used in high-temperature and pressure atmosphere are well known.For instance, currently available gaskets for internal combustionengines are generally broken down into the following two types. One typeis referred to as the steel-best type and it comprises a thin core sheetof a metal plate provided on both sides with a multiplicity of smallprojections. The sheet is applied with a gasketing material on bothsurfaces. A metal mesh material may be used as the core material toobtain a similar gasket. The other type is called the power-best typeand it has a structure in which the arrangement of the aforesaid coreand gasketing material is reversed; in other words, a gasketing materialis applied on both sides but the thin metallic sheet has a number ofsmall projections on only one side.

The core metal, which has a multiplicity of small projections, isusually formed of a soft steel plate, and is about 0.15 to 0.30 mm inthickness. Each individual projection, which may take on various shapessuch as rectangle, square, triangle or (inverted) trapezoid, passesthrough the gasketing material with its projecting point being foldeddown for retainment thereof.

The metallic mesh material used as the core is generally formed byplain-weaving of metal wires, such as soft or stainless steel wires,which have a diameter of about 0.2 to 0.5 mm.

Frequently used for the gasketing material is a sheet which is obtainedby a known paper-making method from a slurry in which synthetic rubberor resin is bonded to asbestos fibers in water. In lieu of the sheetthus obtained, it has also been proposed to apply a combination ofnon-metallic organic fibers with metal fibers and boron nitride, or ofasbestos fibers with flakes of graphite or mica powders, rubber,vulcanizers and fillers. It is also known to use as the gasketingmaterial a sheet material of expanded graphite or a compound obtained bykneading together asbestos fibers, synthetic or natural rubber,synthetic resin, inorganic fillers, etc., with an organic solvent suchthat it has an appropriate viscosity. In the latter instance, thecompound is coated onto the core material by means of friction rolls toform thereon a film having a desired thickness. Such film is dried uponremoval of the solvent.

The gasketing material is then blanked into a given shape, and providedwith a grommet or metal ring which is designed to prevent an escape ofcombustion gas prevailing in a cylinder bore portion. In this manner, agasket is obtained which is suitable for use in, for example, thecylinder head of an internal combustion engine. Most of the gasketingmaterials referred to above comprise a compound consisting mainly ofasbestos fibers in order to take advantage of the good propertiesthereof, i.e. chemical resistance, flexibility, physical resistance,etc. However, the asbestos fibers (chrysotile asbestos) havedisadvantages since they slowly give off water of crystallization at atemperature of approximately 400° C. with an attendant deterioration inproperties. This leads inevitably to reductions in strength andflexibility.

To provide a solution to such a deterioration problem, various proposalshave been made. However, there are no studies about the development of agasketing material in which the physical resistance and flexibility arekept intact, even at a temperature region exceeding the aforesaidtemperature. A sheet of expanded graphite, which was proposed as areplacement for the asbestos gasket, has a disadvantage similar to thatof the asbestos fibers. It starts to undergo oxidation at atemperature=of about 400° C. in an oxidative atmosphere, and is sublimedif oxldation is continued for an extended period of time. Difficultiesare also encountered in the preparation of a gasket sheet from a sIurryin which a gasketing material is dispersed in water, or a compoundthereof having a suitable viscosity controlled by an organic solvent.This is because voids are left in the sheet, upon removal of the wateror organic solvent, by evaporation, and drying steps which cannot beomitted. Such voids may amount to 40 to 50% by volume of the sheet. Toreduce the void volume, an attempt was made to press or roll out thesheet while a core material or other material was combined therewith toform a composite product. It should be noted that the voids are presentin fiber entanglements as an aggregation of numerous fine pores ratherthan as a few macropores. Therefore, it is very difficult to close upsuch fine pores by pressing the sheet in a dry state which issubstantially free from solvent. In other words, such fine pores stillamount to as many as 10 to 20% by volume of the gasket sheet, even uponcompression, and provide passages through which a fluid leaks.

On the other hand, the cylinder head of an internal combustion engineshould be sealed simultaneously, with the use of a single gasket,against transmission of three fluids, i.e., combustion gas of fuel,lubricating (engine) oil for the lubrication of mechanical parts, andcooling liquid (water) for cooling hot combustion gas. This singlegasket is then required to have a so-called semi-metallic structure, inwhich it is covered with a grommet in order to seal the circumference ofa cylinder bore portion against transmission of hot combustion gas. Anopening for cooling water and lubricating oil is sealed by a compositegasketing material as blanked. A sheeting for the gasket for such acylinder head is incorporated with fillers bonded by rubber (usually,oil-resistant synthetic rubber).

Reference will now be made to a vortex gasket, which is a modifiedversion of the aforesaid gasket. Most of the vortex gaskets of the typeused currently are constructed as follows: A metal hoop material,obtained by forming a stainless hoop into a V- or W-shape, issuperimposed upon a filler material which is obtained by forming ashock-absorbing packing material of, for example, asbestos paper, into asimilar shape. The obtained composite product is wound spirally, withthe beginning and terminal ends being spot-welded.

The hoop material forming part of the vortex gasket is generally made ofstainless steel (SUS 304, 321, 316), due to its good heat, chemical, andphysical resistance. For this special purpose, SUS 316-L and 316-LEC,which are also alloys of stainless steel, or other substances such astitanium, Monel and Inconel may be employed.

The most usual filler material is asbestos paper. PTEF, in particular,is employed in a case in which chemical resistance is of importance. Dueto its heat and chemical resistance, natural graphite is also used inthe form of an expanded graphite sheet. For this special purpose, usemay be made of an asbestos joint sheet, which is superior in sealingcharacteristics relative to the asbestos paper.

With the vortex gasket of the aforesaid structure, the edges of the hoopmaterial formed into a V- or W-shape come in tight contact with thesurfaces of the parts joined therethrough, and seal them againsttransmission of fluid in a metal-to-metal contact manner. At the sametime, the filler material rolled in between the hoop material functionsas a cushion, in combination with the denseness thereof and the width ofthe contact surfaces of the parts. In this manner, the filler materialaids the impact resistance of the hoop, and seals the parts againsttransmission of a portion of the fluid which still leaks. Such a sealingmechanism is repeatedly developed to achieve sealing againsttransmission of the fluid.

The vortex gasket, working on the sealing principle (mechanism) asmentioned above, requires a relatively large clamping force in view ofthe need for making a metal-to-metal contact more tight. A main use ofthe vortex gasket is in sealing a high-pressure and -temperature regionagainst transmission of fluid.

In general, the vortex gasket is fundamentally formed into a ring shapedcross-section, and may be formed into a special shape in cross-section,such as oval, track, diamond or rectangular shape, depending upon thepurpose. When simultaneously sealing a certain apparatus, such as a heatexchanger, against transmission of a plurality of fluids with the use ofa single vortex gasket, the latter may be of a so-called branched type,in which the basic version of vertex gasket is modified in such a waythat its inside is divided into two or three parts corresponding to theflanges to which it is to be joined.

The main use of most of the vortex gaskets is that of sealing ahigh-temperature and -pressure region against transmission of fluid, andthey are provided with inner and outer reinforcing rings capable ofresisting the fluid pressure. At the same time, these rings are designedto serve as a compression gauge having an outer diameter and a thicknesssufficient to maintain centering and keep the amount of clampingconstant when the gasket is joined to associated flanges. As a result,the vortex gasket is clamped in the optimum state.

The vortex gasket, as characterized above, is used mainly in chemicalplants and apparatus as a seal resistant to high-temperatureand-pressure; however, the range of its use is now increasing to includeits use as a low-pressure seal.

As mentioned above, asbestos paper is most generally used as the fillermaterial for the vortex gasket. Asbestos fibers (chrysotile asbestos,forming a major part of asbestos paper, begin to lose the water ofcrystallization contained in their tissue at temperatures of 400° to500° C. At about 800° C., substantially all the water ofrecrystallization is eliminated so that the fibers undergo degradation.Due to its lack of resiliency in a high-temperature region, the asbestospaper suffers increasing torque losses, which results in markeddeterioration in the sealing characteristics of the vortex gasket.

Since the asbestos paper is a fibrous material, a filler material whichis composed mainly thereof is deficient in denseness, and encountersextreme difficulty in sealing various parts against transmission offluids, especially gases.

In addition, the asbestos fibers are dug out of the ground with chlorineions (Cl⁻) and magnetite being contained therein. A technique forcomplete separation of such chlorine ions and magnetite from theasbestos fibers has not been developed up to now. Accordingly, asbestospaper using asbestos fibers is still contaminated with these substances.Surprisingly, the asbestos fibers may have a chlorine ion contentexceeding 1,000 ppm depending upon the place of production.

The vortex gasket is mainly used for sealing a high-pressure and-temperature region against transmission of fluids, as mentioned above,and most of the equipment and piping applied to such a region are formedof stainless steel. When the vortex gasket comes in contact withassociated flanges of stainless steel, there is always a possibilitythat the presence of large quantities of chlorine ions and magnetitecontained therein will pose problems in connection with corrosion, forexample, electrolytic or pin-hole corrosion, of the stainless steel.

However, asbestos fibers which are white or light-green inorganic fibersexpressed by the following empirical formula: Mg₃.Si₂ O₅ (OH)₄, haveadvantages. They have a rather small diameter, in the order of 0.000033mm, are rich in flexibility, possess strength on the order of 190 to 330kgf/mm², and have a greater tensile strength than that of steel, and arestable as well as resistant relative to many chemicals. This is why agasketing alternative to the asbestos fibers has not been substantiallyintroduced up to now.

Despite the fact that asbestos fibers are deficient in high-temperatureresistance substantially over its entire range of applicability, theyare now reluctantly used as a gasketing material. However, the asbestosfibers encounter limitations, or even difficulties, in use due to theiradverse influence upon the human body.

As mentioned above, the vortex gasket was originally designed for use inthe sealing of a high-temperature and -pressure region, and is nowavailable in the sealing of a low-pressure fluid region as a result ofits stability. Parts of equipment or piping applied to such alow-pressure region are designed to have a strength corresponding to thepressure or pressure rating of a working fluid. However, it isimpossible to obtain a clamping force sufficient to permit a completemetal-to-metal contact of the hoop with the flanges to which they are tobe joined, with the result that the vortex gasket does not operate onthe intended sealing mechanism. Under such conditions, it is impossibleto attain complete sealing unless the filler material fills up anunsatisfactory metal-to-metal contact. Consequently, it has now beenfound that the properties of the filler material play an important role.

Recently, a sheet of expanded graphite was proposed as a unique fillermaterial which is equivalent to asbestos. Although this sheet hassufficient denseness to fulfill the abovementioned requirements, it isvery expensive. This sheet also has a disadvantage. It undergoesoxidative sublimation upon being heated to more than 400° C. in anoxidative atmosphere, and so is not put to practical use.

Although a sheet of fluorine resin has been proposed as well, it meetsonly the chemical resistance requirement since it is a thermoplastic,polymeric material which is essentially of no avail in the area ofhigh-temperature resistance.

Thus, there is a strong demand for the development of a gasketingmaterial which is inexpensive, but yet is equivalent in variousproperties to asbestos fibers.

It is an object of the present invention to eliminate the drawbacks ofthe prior art gaskets. It is therefore a main object of the presentinvention to provide a gasket or vortex gasket which can retain itsstrength and resiliency, even at a temperature exceeding 400° C.

These and other objects and advantages of the present invention willappear more clearly from the following specification with theaccompanying drawings, in which:

FIG. 1 is a graph showing the physical properties of the inventive andprior art gaskets for the purpose of comparison;

FIG. 2 is a plan view showing one embodiment of the gasket according tothe present invention;

FIG. 3 is a partially enlarged section of the gasket of FIG. 2;

FIG. 4 is a sectional view of filler embossing rolls for theillustration of the method for the production of a conventional vortexgasket;

FIG. 5 is a side view of a hoop and a winding mandrel;

FIG. 6 is a side view showing the winding mandrel for winding the hoopsuperimposed on the filler;

FIG. 7 is a side view of the embossed filler;

FIG. 8 is an end view of the construction of a vortex gasket;

FIG. 9 is a partial side view of a laminate of a filler and a metal web;

FIG. 10 is a side view of the embossed laminate;

FIG. 11 is a view illustrative of the distribution of clamping pressuresof the inventive vortex gasket;

FIG. 12 is a view illustrative of the distribution of clamping pressuresof the prior art vortex gasket; and

FIG. 13 is a side view of an apparatus for producing the inventivevortex gasket.

The gasket according to the present invention, is characterizedprimarily in that it comprises a sheet obtained from a compositionconsisting of 40 to 80% by weight of thin flakes of expandedvermiculite, 1 to 30% by weight of fibers, 5 to 40% by weight of fillingfine grains, and appropriate amounts of a binding agent and avulcanizing agent, and a metal plate laminated thereon. The gasket is acomposite product which has therein a minimum of voids and hence agreatly improved sealing effect. The method according to the presentinvention, is characterized primarily in that a vortex gasket is formedby spirally winding a metal hoop together with a filling material, andthe filling material is composed mainly of expanded vermiculite. Thisvortex gasket can exhibit a stable sealing effect even in a low clampingpressure region.

First of all, vermiculite used as a main material in the presentinvention will be explained.

Substances generally known as flake structures include mica andgraphite, in addition to vermiculite. A known method carried out toexpand these substances in a flake-like manner comprises, for instance,impregnating chemicas in between the flakes thereof and heating the thusimpregnated masses to a temperature at which decomposition of thechemicals takes place, thereby obtaining an expansion force sufficientto cause separation of the flakes from each other. An industriallyavailable method for the expansion of vermiculite, on the other hand,involves rapidly exposing it to a high-temperature atmosphere, e.g.,placing it in a rotary kiln maintained at near 100° C. The interlaminarwater of crystallization in the flake structure then evaporates rapidlyas a result of the formation of an expansion pressure which permitsseparation of the flakes from each other. The former method requirestroublesome chemical-treating and drying steps, and is more expensivethan the latter method. Therefore, the latter method is generally usedfor the production of industrial materials, such as aggregates for heatinsulation, spraying materials, materials for modifying paints, etc.

This is why the expanded vermiculite is selected from the flakestructures in the present invention.

Vermiculite has a structure resembling black mica belonging to athree-layer mineral, and is expressed in the pure form by the followingstructural formula according to I. Barshad (1948): ##EQU1##

Upon being heated to 700° C. or higher, the vermiculite starts for thefirst time to lose its water of crystallization (water contained in thecrystal). Thus, the vermiculite has an advantage over the asbestosfibers in heat resistance, since the latter gives off the water ofcrystallization at a lower temperature of about 400° C.

The vermiculite, as expanded in the foregoing manner, is larger involume than the original vermiculite by a factor of 5 to 20. It providesa very weak and fragile sheet, even if the particles of such expandedvermiculite are physically bonded to each other. This is because thesurface of the bonded particles have an extremely low strength. However,with the flakes separated from the expanded vermiculite by applying ashearing force on the vermiculite dispersed in water with the use of ahigh-speed mixer or by applying a shearing force on the vermiculite in adry state with the use of a disintegrator such as miracle mill, it hasnow been found by experimentation that a flexible but firm sheet isobtained by bonding the thus separated flakes with each other at theiractivated surfaces.

To afford strong activity to the surfaces of the separated flakes, ithas been ascertained that they should preferably be 10 to 60 meshes indiameter and no more than 100 microns in thickness.

With a composition composed mainly of thin flakes of expandedvermiculite and further including fibers, finely divided particles,binders and vulcanizers, it is possible to obtain a gasketing sheet inwhich are filled, in the densest state, the thin flakes of vermiculite,the fibers and the finely divided particles which are different in shapefrom one another. Since the prior art gasketing sheet, which wascomposed mainly of fibers, cannot be put in the densest state, it isimpossible to decrease the number of finally remaining voids or pores.This leads to deterioration in the sealing characteristics of thegasket.

In the following table, the denseness of the composition composed mainlyof thin flakes of vermiculite and further including fibers and finelydivided particles is shown in terms of bulk density according to JIScylinder method. The table also sets forth that of the prior artfiber-filled sheet for the purpose of comparison.

                  TABLE                                                           ______________________________________                                                                       Bulk Density to                                       Fibers                                                                              Particles Flakes  JIS cylinder method                            ______________________________________                                        Prior Art                                                                              70%     30%       --    1.31 g/cm.sup.3                              Composition                                                                   Prior Art                                                                              60%     20%       20%   1.35 g/cm.sup.3                              Composition                                                                   Prior Art                                                                              30%     30%       40%   1.43 g/cm.sup.3                              Composition                                                                   Inventive                                                                              10%     30%       60%   1.54 g/cm.sup.3                              Composition                                                                   Inventive                                                                               1%     19%       80%   1.58 g/cm.sup.3                              Composition                                                                   Inventive                                                                               0%     10%       90%   1.50 g/cm.sup.3                              Composition                                                                   ______________________________________                                    

As a result of the abovementioned experiments, it has been found thatthe composition having the greatest effect on the denseness of theinventive product contains 40 to 80% by weight of thin flakes ofvermiculite, 5 to 40%, preferably 19 to 30%, by weight of finely dividedparticles, and 1 to 30% by weight of fibers. It will be understood thatthose skilled in the art may easily determine the range of eachcomponent added depending upon the purpose.

The fibers used in the present invention include any suitable fibersexcept asbestos fibers, such as non-metallic inorganic fibers and metalfibers. Although it has heretofore been considered that difficulties areencountered in preparing a sheet with the use of only non-metallicfibers, it is possible in the present invention not only to use suchnon-metallic fibers as carbon fibers, phenol fibers or ceramic fibers,but also to use metal fibers such as stainless steel fibers or brassfibers.

The gasket for an internal combustion engine, which uses the aforesaidfibers, has the advantage that heat generated by explosion andcombustion of fuel escapes through a metal grommet applied over acylinder bore portion into a cooling water discharge port along areinforcing metal plate. A disadvantage of the conventional gasket,comprising a main gasketing material incorporated with asbestos fibers,is that the heat of combustion is accumulated causing increasingdeterioration in the physical properties. This is because the asbestosfibers have a low heat conductivity and have difficulty conducting heat.However, both the non-metallic fibers such as glass fibers and the metalfibers such as stainless steel fibers used in the present invention havea heat conductivity greater than that of the asbestos fibers, and permita positive escape of heat even from the sheet portion. In particular,use of the metal fibers such as stainless steel fibers have asynergistic effect on the heat resistance of vermiculite, resulting in agreat increase in thermal resistance. For the purpose of comparison, theheat conductivity, tensile strength and changes in tensile strength uponheating of the inventive and prior art products are set forth in thefollowing table.

                  TABLE                                                           ______________________________________                                                  Invention                                                                              Prior Art                                                  ______________________________________                                        Heat        Kcal/mh °C.                                                                       Kcal/mh °C.                                     conduc-     0.181      0.210                                                  tivity                                                                        Tensile     63 kg f/cm.sup.2                                                                         107 kg f/cm.sup.2                                      Strength                                                                      Changes in tensile                Heating                                     strength upon                     Temperature                                 heating       0%         0%       Normal                                                                        Temperature                                             +80%       +20%       100° C.                                          +70%       +17%       200° C.                                          -45%       -30%       300° C.                                          -40%       -23%       400° C.                                          -28%       -25%       500° C.                                          -26%       -21%       600° C.                              ______________________________________                                    

The gaskets according to the present invention can be made in variousmethods.

In particular, the starting composition can be formed into a sheet byeither one of the coating and extrusion processes of the papermakingtype. Thus, a high-performance sheeting can be manufacturedinexpensively and easily with no need for special equipment.

The sheeting is laminated upon a reinforcing metal plate to form acomposite sheet. When the composite sheet is then pressed or rolled outin a wet (semi-dry) state, the thin flakes of vermiculite are orientatedin the planar direction of the sheet, so that the flakes, the fibers andthe fine filling particles are put in the densest state. At the sametime, the activated lamination planes of the discrete thin flakes arepermitted to re-contact or come into engagement again with each other,thereby affording flexibility to the sheet. Such flexibility is notattained in the conventional sheet. The results of flexibility testingcarried out according to JIS R 3453 are given in the following table.

                  TABLE                                                           ______________________________________                                                Prior Art                                                                             Prior Art                                                                              Inventive  Inventive                                         Sheet-  Sheet-   Sheet-     Sheet-                                            ing (A) ing (B)  ing (C)    ing (D)                                   ______________________________________                                        Flexibility (F)                                                                         27        15       1        0.3                                     ______________________________________                                    

In the table, a value F for flexibility is understood to mean a ratio ofthe diameter of a round metal rod to the thickness of a sample, whereinno crack or fissure is observed in the sample wound 180° around the rod.A lower value indicates a higher flexibility.

The graph of FIG. 1 shows a relationship between the density and tensilestrength of a sheet which is especially rolled out or pressed in a wetstate in order to orientate thin flakes in the planar direction thereof.For the purpose of comparison, FIG. 2 also relates to a case in which asimilar sheet is pressed in a dry state.

When the composition according to the present invention is pressed, thethin flakes are orientated in the planar direction of the sheet with anattendant increase in density, so that the activated lamination planesof the flakes are brought into re-contact with each other with a bindingforce, thus resulting in an increase in tensile strength. It can be seenfrom FIG. 1, however, that the sheet pressed in a wet (semi-dry) statehas a far greater tensile strength, at the same density, than that ofthe sheet pressed in a dry state. This is due to the fact that theactivated lamination planes of thin flakes are placed in a wet statethat assures a more actively binding effect. The resulting tensilestrength is thus said to be a major breakthrough that is, for the firsttime, realized through a synergistic action with the closest packingeffect of the composition as previously discussed. It is here noted thatif a sheet remaining wetted is superimposed on a reinforcing metalplate, and the thus obtained composite sheet is rolled out or pressed assuch, an amount of water is squeezed out of the sheet by a pressingforce with the consequence that the sheet flows. This may render anincrease in density difficult. However, the density can easily beincreased by pressing the composite sheet while absorbing the squeezedout water in filter paper, woven fabric or a blanket interposed betweenit and the roll or press.

The gasket of the present invention can be applied to the cylinder headof an internal combustion engine with advantages which will now beexplained.

As previously described, the cylinder head of an internal combustionengine should be simultaneously sealed against transmission of threefluids, i.e., combustion gas of fuel, lubricating (engine) oil for thelubrication of mechanical parts, and cooling water for removing the heatof combustion gas with the use of a single gasket. Accordingly, thegasket is designed for each of the requirements which vary as a functionof the properties of these fluids. For instance, a cylinder bore isrequired to have a semi-metallic structure, in which the gasket iscovered with a metal grommet in order to seal it against transmission ofhigh-pressure and -temperature combustion gas, and an opening forcooling water and lubricating oil is provided with a composite gasketingmaterial as blanked. This is a basic structure for generally availabecylinder heads. However, a cast aluminum alloy has recently beenintroduced as a cylinder head material for a reduction in the overallweight of the engine, an increase in cooling efficiency, and otherconsiderations. Such a material poses problems in connection with thestructural strength of the aluminum alloy; limitations are placed uponthe amount of clamping force to be applied on the gasket for thecylinder head; and the cylinder head suffers deformation with a localdeficiency of the clamping pressure.

These phenomena seem to happen in different ways if viewed from anotherangle. Consequently, investigations are carried out on clamping pressureapplied to each individual internal combustion engine. When a deficiencyof clamping pressure is then detected, a sealing material compatiblewith the surface of a flange is locally applied, such as by dipping,coating or padding.

According to the gasket of the present invention, however, the sheetingmaterial is composed mainly of thin flakes and a minor amount of fibermaterials and finely divided grains in the closest packing state, andhas the thin flakes orientated in the planar direction thereof. Thisassures that the gasket has good sealing characteristics which areattributable to its high flexibility and which are not all attained inthe prior art gasket composed mainly of a fibrous material, and itundergoes little or no decrease in strength even upon exposure to anatmosphere in excess of 400° C. with sustained elasticity or resiliency.Since the gasket of the present invention is capable of preventingdeterioration in sealing and torque characteristics due to thermaldegradation, it can surely seal the cylinder head of an internalcombustion engine against transmission of the aforesaid three fluids.

In addition, the use of non-metallic fibers (glass, carbon or similarfibers. and metal fibers (stainless steel, brass or similar fibers) asan alternative to asbestos fibers is effective not only in theelimination of the adverse influence, upon the human body, of asbestosdust generated during handling, but also in the improvement of thecooling efficiency of the engine and of the durability of the gasketsince the metal fibers serve as a mediator for the transmission of heat.

The gasket of the present invention, which is typically applicable tointernal combustion engines, has great economical advantages over theprior art in that it can be fabricated on existing equipment, with noneed of specially designed apparatus, by using expanded vermiculite,which is inexpensive, as a main starting material.

The present invention will now be explained with reference to a vortexgasket.

According to the present invention, a vortex gasket is also provided, inwhich there is packed or filled a sheet formed from a mixture of theaforesaid discrete expanded vermiculite with unexpanded vermiculite.When this gasket is mounted on an associated flange and put in ahigh-temperature atmosphere, the unexpanded vermiculite is expandedunder the action of the heat causing further increase in the packing orfilling density between the hoop. At the same time, the resultingexpanding force acts as a reaction force that gives rise to anaugmentation of the impact resilience of the gasket, and leads toenhanced sealing characteristics thereof.

It will, of course, be understood that for more satisfactory impactresiliency, it is advantageous to impregnate, in advance, the unexpandedvermiculite with an expanding agent which decomposes at a temperaturebelow the service temperature of the vortex gasket. For the expandingagent, preference is given to, for example, an aqueous solutioncontaining nitrate ions and ammonia ions.

Further increases in strength and flexibility may be attained byincorporating non-metallic fibers, metal fibers, binders, fillers, etc.,in addition to the expanded vermiculite in the sheet material.

The vortex gasket according to the present invention can be manufacturedin the same manner as that applied in the production of the prior artvortex gasket in which asbestos is used for a sheet material.

A general method for the production of vortex gaskets will now bebriefly explained.

As shown in FIG. 4, a sheet 1 of asbestos paper having a given thicknessis cut off to prepare a filler material having a width of about 5 mm,while it is embossed by means of a set of roll shear cutters 2a and 2b.A hoop material is also embossed by similar means. As shown in FIG. 5,one end of the embossed hoop 3 is first fitted into a groove in awinding mandrel 4 of a winding machine. Two or three turns of the hoopare provided on the mandrel, followed by spotwelding. Then, as shown inFIG. 6, the embossed filler materials 1 of asbestos paper are insertedinto the hoop 3, and are wound together with the hoop to provide a givengasket width. After the filler material 1 is cut off, two or three turnsof the hoop material 3 alone are provided, followed by spot-welding inthe same manner as mentioned above. The thus spirally wound gasket isremoved from the mandrel, and unnecessary portions of the hoop materialare cut off, leaving openings for the insertion of a slit, etc.

FIG. 7 is a partial section showing the filler material forming part ofthe vortex gasket. Usually, elongation of the filler (of asbestos paper)takes place when it is being embossed and cut off with the roll cutters,so that a crack or crevice is formed in a portion indicated at A. Such acrack is left as a deficient portion, in which packing is insufficient,in the spirally wound gasket (see FIG. 8). This is particularlypronounced in the filler material which is composed mainly ofvermiculite.

Such a deficient portion provides a fluid channel, extending spirallyfrom the inside to the outside of the gasket, which is responsible fordeterioration in the sealing characteristics.

However, if the filler material is provided with a material capable ofovercoming a tensile force which may be exerted by the roll cutters inthe step of embossing the filler material, the occurrence of such adeficient portion as exemplified by a crack or crevice can then beavoided during the embossment of the filler material.

As shown in FIG. 9, a soft metal web 5 can be laminated upon the fillermaterial 1 to form a composite sheeting, which is, in turn, embossedinto a V- or W-shape from the outside of the web, by means of the rollcutters. The metal web may be formed of aluminum, copper, babbit metal,nickel, silver, gold, etc, and preferably has a width of 0.2 mm or less.

In general, the soft metal web formed of aluminum, babbit metal, etc.,has a tensile strength greater than that of the filler material, andexhibits a lower elongation in the width direction of the fillermaterial when a tensile force is applied thereto during embossing. Anoverall elongation of the composite sheeting is smaller than that of thesheeting which consists only of a filler material. Such a reduction inthe overall elongation causes the filler material to be withdrawn justbefore the roll cutters, as indicated by arrows in FIG. 10.

This assures that a crack or crevice is not formed in the portion A ofthe filler material having a soft metal web laminated herein, even underthe action of a tensile strength. In addition, since the embossing iseffected mainly on the soft metal web, the resulting composite sheetinghas a rather small curvature and its compactness and denseness isexcellent.

With respect to the clamping pressure, which is one of the importantfactors for the estimation of sealing characteristics according to thepressure-sensitive sheet method, measurements were carried out on theinventive vortex gasket in which the filler material of vermiculite wasobtained by the abovementioned embossing step and on the prior artvortex gasket. From the results shown in the following table and FIGS.11 and 12, it has been found that, in the inventive gasket, the fillermaterial has an improved denseness with a good pressure distribution inwhich there is only a little difference between the pressures applied inthe hoop 3 and the filler 1.

                  TABLE                                                           ______________________________________                                                      Prior Art                                                                             Invention                                               ______________________________________                                        Crack or Crevice in                                                                           Observed  Same                                                Portion A                                                                     Packing Density of                                                                            1.47 g/cm.sup.3                                                                         1.76 g/cm.sup.3                                     Filler                                                                        ______________________________________                                    

A vortex gasket, in which a hoop material is tightly joined to a fillermaterial having a good flexibility, is obtained by applying a hydrouscomposition consisting mainly of expanded vermiculite on the hoopmaterial, followed by drying, which permits direct embossing of the thusobtained laminate of the filler and the hoop.

As mentioned above, vermiculite is a hydrous silicate mineral as will beunderstood from I. Barshad's structural formula (1948), and has a largequantity of water of crystallization in its flaky interlaminarstructure. The interlaminar wate of crystallization is dispersed andevaporated rapidly upon being heated rapidly to elevated temperaturesand generates a force sufficient to permit separation of the flakes fromeach other. As a result, successively expanded vermiculite in the formof a green caterpillar is obtained.

It is also known that similar expanded vermiculite is obtained byallowing permeation of a peroxide, such as hydrogen peroxide, and theaforesaid chemicals into the flaky layers, and heating them to atemperature at which rapid scattering of the chemicals is promoted (thistemperature is usually lower than that at which scattering of theinterlaminar water occurs.).

The thus expanded vermiculite is dispersed in water and sheared at highspeeds to obtain thin flakes. The flakes are then adjusted in such amanner that they have a diameter of 246 microns (60 meshes) to 165microns (10 meshes), and are formed into a sheet by means of apaper-making method. Such sheet possesses a degree of flexibility thatis unattainable in the prior art. This is due to the following fact.

The thin flakes obtained by shearing of expanded vermiculite havelamination planes which were initially bonded to each other. Stillactivated in the form of thin flakes, these planes are recombined witheach other in the sheet-making step so that a sheet excelling inflexibility is obtained.

As mentioned above, however, the method comprising the steps of applyinga hydrous composition of flaky vermiculite used as a filler on a hoopmaterial and pressing the filler during embossing has an advantage overthe sheet-making method in that the number of the activated planes offlakes orientated in parallel increases. This results in the formationof a filer which is excellent in both bonding force and flexibility. Inaddition, since pressing is effected during the course of embossing, anypressurizing treatment of vermiculite can be omitted.

As previously mentioned in connection with the preparation of expandedvermiculite, it is preferable to use chemically treated vermiculitesince flakes retaining an amount of water of crystallization can beobtained therefrom.

The surface activity of the thin flakes acts not only on the flakes perse, but also on the surface of a metal. Although varying in magnitudedepending upon the surface smoothness of metals, the bonding forceresulting from this activity can act on all kinds of metals. However,with respect to metals, fabrics or blankets which have irregularities onthe surface, such a force is very weak.

The present invention will now be explained with reference to thefollowing non-restrictive examples. Examples 3 and 4 relate to thevortex gasket.

EXAMPLE 1

A grade No. 3 vermiculite ore was rapidly fired and expanded at 900° C.in a rotary kiln to prepare expanded vermiculite. This vermiculite wassheared at high speed in a disintegrator to obtain thin flakes having adiameter of 50 meshes and a thickness of 35 microns. 41 kg of the thinflakes of vermiculite were dispersed in 1000 liters of water, togetherwith 4 kg of glass fibers having a diameter of 12 microns and a lengthof 100 mm and 22 kg of clay having a particle size of no more than 7microns. To the resultant dispersion (slurry) was added, underagitation, 4 kg of synthetic rubber latex and 0.3 kg of a vulcanizingagent. It was then processed in a paper machine and dried, therebyobtaining a vermiculite sheeting having a thickness of 1.5 mm and a bulkdensity of 0.78 g/cm³. This sheeting was laminated, while subjected toforce, on both surfaces of a thin soft steel plate having a thickness of0.2 mm and being provided on both sides with triangular projections. Thethus obtained composite sheet was embossed and rolled out by a pressingroll to orientate the thin flakes in the planar direction of the steelplate. In this manner, a gasketing material comprising a sheet having adensity of 1.5 g/cm³ and an overall thickness of 1.8 mm was obtained.This material was blanked into a customarily available shape, and wasprovided on its cylinder bore portion with a grommet of stainless steel(SUS 304) having a thickness of 0.22 mm in order to obtain a gasket forthe cylinder head of an internal combustion engine.

As shown in FIGS. 2 and 3, the obtained gasket comprises a sheeting 1'of vermiculite, a thin metal plate 12 for reinforcement, a cylinder boreportion 13 which is provided with a grommet 14, an opening 15 forcooling water, an opening 16 for lubricating oil which is provided witha grommet 17 and a bolt bore 18. This gasket was assembled to thecylinder head of an automotive internal combustion engine by clamp boltswith a torque of 800 kgf-cm. It was then subjected to a cyclicdurability test on a bench under the condition that the engine wasforcibly cooled with cooling water at 6000 rpm. The results weresatisfactory, as is shown in the following table.

    ______________________________________                                        Results of Cyclic Durability Test                                             ______________________________________                                        Sealing Pressure for Cooling Water                                                                    5 kgf/cm.sup.2 G                                      Sealing Pressure for Lubricating Oil                                                                  7 kgf/cm.sup.2 G                                      Sealing Pressure for Combustion Gas                                                                   45 kgf/cm.sup.2 G                                     Torque Down             7%                                                    Compression Rate        18%                                                   Trace of Unusual flow   none                                                  ______________________________________                                    

EXAMPLE 2

A grade No. 2 vermiculite ore was rapidly fired and expanded at 900° C.in a rotary kiln to prepare expanded vermiculite. 55 kg of the expandedvermiculite, together with 150 liters of water, were charged in aHenschel mixer, and were sheared at high speed in water in order toprepare an aqueous slurry of thin flakes having a thickness of 23microns. This slurry was passed into a machine chest to which 1350liters of water were added. To this slurry were also added 2 kg of pulp,8 kg of stainless steel having a length of 12 microns, and 37 kg of clayhaving a diameter of no more than 7 microns in order to prepare auniform dispersion. To the obtained dispersion or slurry there wasadded, under agitation, 5 kg of synthetic rubber latex and 0.4 kg ofvulcanizing agent. This was slowly added while continually agitatingwith a sulfuric acid band having a concentration of 5% until the latexwas completely fixed. The resulting slurry was processed in a papermachine to prepare a sheeting being 2 mm in thickness. This sheeting wassuperimposed, while subjected to force, upon both surfaces of a softsteel plate having a thickness of 0.25 mm and being provided on bothsides with rectangular projections such as those of a grater. Theobtained composite sheet was pressed, on a hydraulic press, into a statewherein it was covered on both sides with a blanket, thereby squeezingthe water therefrom. This sheet was dried in an oven maintained at 110°C. to obtain the gasketing material. This material was blanked into acustomarily available size, and was provided with a cylinder boreportion, an opening portion for lubricating oil, and a portioncorresponding to a chain case with a grommet of soft steel having anSPCC thickness of 0.2 mm and a width of 3 mm, a grommet of copper havinga Cup thickness of 0.15 mm and a width of 2 mm, and a film 19 treatedlocally by means of a synthetic resin sealing agent and having athickness of 0.05 mm (see FIG. 2). In this manner, a gasket for thecylinder head for an internal combustion engine was fabricated.

The obtained gasket was assembled relative to the cylinder of anautomotive internal combustion engine by means of clamp bolts with atorque of 750 kgf-cm, and was subjected to 50 cycles of simulationtesting; one cycle involving 30 min. heating using vapor directed from aboiler to a cooling water passage, ard 30 min. cooling using tap water.The results were satisfactory, as is shown in the following table.

                  TABLE                                                           ______________________________________                                                          Invention                                                                            Prior Art                                            ______________________________________                                        Weight Loss upon Intense Heating                                                                  13.4%   18.4%                                             Stress Relaxation   17%     26%                                               Water Leak Testing (measured after 50 cycles of simulation testing)           1.0        kfg/cm.sup.2 G                                                                             No leak  No leak                                      2.0                     "        "                                            3.0                     "        "                                            3.5                     "        Leak observed                                4.0                     "        "                                            4.5                     "        "                                            5.0                     "        "                                            ______________________________________                                    

As stated above, the gasket of the present invention has good sealingcharacteristics which are sufficient to seal the cylinder head of aninternal combustion engine against transmission of three fluids, i.e.,combustion gas, lubricating oil, and cooling water. It can also retainits strength and resiliency, even at a temperature in excess of 400° C.,and can be used for an extended period of time without difficulty.

EXAMPLE 3

A grade No. 3 vermiculite ore was treated with 10% hydrogen peroxide.100 parts of the thus expanded vermiculite were sheared at high speed ina mixer, together with double amounts of water, for 10 minutes in orderto prepare thin flakes. To the flakes there were added, under ampleagitation, 10 parts of unexpanded vermiculite, 3 parts of glass fiber,and 17 parts of clay to produce a slurry to which were added, whilemixing at a low speed, 5 parts of synthetic rubber latex and 0.5 partsof a dispersion of a vulcanizing agent. The thus obtained dense slurrywas applied up to a given thickness on a metal hoop 3 by means of acoater 6 as shown in FIG. 13. Making use of the fact that the thinflakes show good adhesion to the hoop but poor adhesion to the blanket,excessive water was squeezed out of the composite sheeting by ablanket-made caterpillar 7 and a suction box 8. The sheeting was thendried in a drying chamber 9, was pressurized by pressing rolls 10 insuch a manner as to orientate the thin flakes in the planar direction,and was embossed and slitted by means of roll cutter 11. The sheetingwas thereafter spirally wound to prepare a gasketing material. To attainmore satisfactory orientation of the thin flakes, friction rolls wereemployed as the pressing rolls. The upper roll (for the coating ofslurry) was rotated in synchronized relation to the running speed of theproduct to be pressed and at a speed faster than that of the upper roll,so that planar forces acted simultaneously on the product to beprocessed.

It is noted that vortex gaskets can be prepared directly without usingthe winding step if the production speed thereof is synchronized to amachine (not shown) for winding the gasketing material.

EXAMPLE 4

Impacts were applied to 7.5 kg of a grade No. 3 vermiculite ore and 31kg of expanded vermiculite that had been rapidly fired and expanded in arotary kiln at 900° C. until most of them were converted into thinflakes having a diameter of 20 to 40 meshes and a thickness of 15 to 30microns, followed by dry separation. The thus separated flakes werecharged into a machine chest together with 3000 liters of water. To thiswas also added 5 kg of linen pulp, which had been immersed in water for24 hours, and 7 kg of bentonite having a particle size of no more than 7microns. The contents of the chest were dispersed by stirring for 15minutes. Stirring was continued with the addition of 8.8 kg of NBR latex(having a solid content of 40% by weight) and 0.7 kg of a vulcanizingliquid dispersion (having a solid content of 10% by weight). Thereafter,0.8 kg of sulfuric acid band (having a solid content of 10% by weight)and 5 kg of Ceparane (having a solid content of 0.2% by weight) wereslowly added for fixation of the latex.

The resulting slurry was formed into a sheet by a paper machine and thendried, thereby forming a vermiculite sheet having a thickness of 0.8 mmand a bulk density of 0.81 g/cm³.

This sheet, with the aid of the embossing roll (FIG. 4) was processedinto a V-shaped tape. This tape was superimposed upon a previouslyV-shaped steel hoop of SUS 304 having a thickness of 0.2 mm and a widthof 4.5 mm, as shown in FIG. 5, and was wound six times in the manner asshown in FIG. 6. After cutting out the vermiculite tape, three turns ofthe hoop line were provided, followed by spot-welding. The obtainedvortex gasket had a 50φ inner diameter, a 61φ outer diameter and athickness of 4.5 mm.

The vortex gasket was mounted by means of three bolts, to a flange,located between an exhaust manifold and an exhaust pipe of theautomotive internal combustion engine of Example 1, with a clampingtorque of 250 kg-cm, and was subjected to durability testing on a benchat 6000 rpm for 20 hours.

The vortex gasket showed no sign of combustion gas leakage. After thetest, the gasket was removed from the flange. The gasket also showed nosign of any unusual appearance.

Compared to the prior art method for manufacturing a vortex gasket bypreparing a hoop and a filler in separate steps and forming them into acomposite sheeting in a later step following by winding, the inventivemethod has a great economical advantage since an inexpensive but stablevortex gasket can be manufactured by means of an energy-saving, highlyefficient, and continuous operation.

As mentioned above, the vortex gasket of the present invention shows notonly good strength, flexibility and compressive resiliency, but alsogreatly improved sealing characteristics, even under a low clampingpressure, due to the high denseness of the filler. Thus, the vortexgasket can be advantageously used as a low-pressure gasket.

According to the present invention, previously troublesome operationscan be converted into a simple, continuous operation with an increase inthe mass-production rate, and inexpensive vermiculite can be used as astarting material. Thus, the present invention is very preferable inview of economic considerations.

According to the present invention, various vortex gaskets of branched,profiled, and double-ring types can be prepared, in addition to thegasket of the basic (doughnut) type.

The present invention is of course, in no way restricted to the specificdisclosure of the specification and drawings, but also encompasses anymodifications within the scope of the appended claims.

What we claim is:
 1. A gasket comprising: a sheet having a compositionof 40 to 80% by weight of thin flakes of expanded vermiculite, 1 to 30%by weight of fibers, 5 to 40% by weight of fine filling grains, andappropriate amounts of a binding agent and a vulcanizing agent; and ametal plate laminated to said sheet.
 2. A gasket as recited in claim 1,in which said metal plate is provided with a plurality of projections.3. A gasket as recited in claim 1, in which the amount of said finegrains ranges from 19 to 30% by weight.
 4. A gasket as recited in claim1, in which said fibers comprise at least one of the group consisting ofpulp, stainless steel fibers, glass fibers, and ceramic fibers.
 5. Agasket as recited in claim 1, in which said thin flakes of vermiculitehave a diameter of 10 to 60 meshes.
 6. A gasket as recited in claim 1,in which said thin flakes of vermiculite have a thickness of no morethan 100 microns.